With respect to a switching power supply used as a power supply of an electronic appliance, there is a demand for a reduction in the loss (heat generation) and an increase in the efficiency. Moreover, also with respect to an image forming device for which load variation is great and which stays in a wait state for a long time, an increase in the efficiency of the power supply device is being studied.
For example, Patent document 1 discloses a switching power supply device which includes a flyback circuit of a diode and a capacitor on a secondary side of a forward converter transformer, and which switches to a flyback method when a load current drops to or below a predetermined value, and extracts energy accumulated in the converter transformer as flyback output.
However, there is a problem that it is difficult to achieve both higher efficiency and miniaturization of the power supply device.